1. Field of the Invention
This invention relates to a double loop antenna, and more particularly, to an antenna printed on a dielectric substance such as a window glass of a motor vehicle for a use to a mobile telephone.
2. Description of the Prior Art
A double loop antenna attached on a glass window of a motor vehicle for use in a UHF band is known. The double loop antenna comprises a pair of semiloop antenna elements with half-wavelength conductors branched from a power feed point in both lateral directions along a grounded conductor, their end terminals are grounded and the feed point is unbalanced power fed (Japanese patent laid open application No. 69704/1987 and U.S. Pat. No. 4,721,964).
FIG. 11 shows a prior art of the double loop antenna which is printed on a rear window glass of a motor vehicle.
In FIG. 11, numeral 1 shows a transmission/reception antenna for an automobile telephone, elements of which are printed on a rear window glass 2 together with defogging heater wires 3 and an antenna conductor 4 for radio (FM/AM) reception. The transmission/reception antenna 1 is arranged along a body of the automobile and consists of a pair of semiloop elements 1a and 1b branched laterally from a power feed point 12a. Both end terminals 1c and 1d of the elements 1a and 1b are grounded so that the feed point 12a is unbalanced power fed from a core conductor of a coaxial feeder cable 7.
This transmission/reception antenna 1 has a sufficient gain and an almost non-directional directivity in a UHF band ranging 850-950 MHz.
The transmission/reception antenna 1 has small dips in directivity for waves coming from sides of the automobile and a defect that gain is slightly lower than a dipole antenna.